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Absolute Risk Reduction Formula:
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Absolute Risk Reduction (ARR) is the difference in event rates between control and experimental groups in clinical trials. It represents the absolute difference in risk between the two groups and is a key measure of treatment effect.
The calculator uses the ARR formula:
Where:
Explanation: ARR measures the absolute difference in event rates between the control group (receiving standard treatment or placebo) and the experimental group (receiving the intervention being studied).
Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed decisions about treatment benefits versus risks.
Tips: Enter both CER and EER as proportions (values between 0 and 1). For example, 0.15 represents 15% event rate. Ensure CER is greater than or equal to EER for meaningful results.
Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while Relative Risk Reduction (RRR) is the proportional reduction in events compared to the control group.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR. It represents the number of patients needed to treat to prevent one additional adverse event.
Q3: What is a clinically significant ARR?
A: Clinical significance depends on the context - the disease severity, treatment risks, and costs. Larger ARR values indicate greater treatment benefit.
Q4: Can ARR be negative?
A: Yes, a negative ARR indicates the experimental treatment is worse than control, which would then be called Absolute Risk Increase (ARI).
Q5: When should ARR be used instead of RRR?
A: ARR is generally preferred for clinical decision-making as it provides the actual magnitude of benefit, while RRR can exaggerate small absolute differences.